An integrated circuit (IC) includes core logic and input/output (IO) circuits. The core logic performs a desired function and requires a low voltage termed as core supply voltage. The IC communicates with other ICs or external devices (filters, sensors etc.) at high voltage range termed as the supply voltage. The IO circuits acts as interface and communicate data between core logic and external devices. The IO circuits are connected to external devices through board traces or metal wires, called transmission lines. An IO circuit includes a main-driver that drives signals on a pad to interface with the external devices. A bidirectional IO circuit has a main-driver used for sending signals to the external devices (transmit mode) and a receiver circuit for receiving signals from the external devices (receive mode).
The IO circuits need to generate output signals to drive external devices, with suitable voltage levels compatible with the specifications of external devices, to ensure that the data is accurately transferred to the external devices. High voltage IO circuits require high voltage output signals to comply with the specifications of the external device. For example, if an external device is designed to receive input signals at +5 Volts, then output signals need to be at a maximum voltage of +5V. However, the high voltage IO circuits are generally implemented using low voltage transistors. In general, using low voltage transistors provides benefits such as high throughput performance, reduced electrical power consumption, lower number of fabrication masks (leading to lower fabrication costs) and high density (number of integrated circuits in a unit area). The low voltage transistors are driven by bias voltages. The use of low voltage transistors in high voltage IO circuit causes coupling of transitions in high voltage output signal to the bias voltages through parasitic capacitances of the low voltage transistors. Stabilizing the bias voltages either requires a large static current or a large capacitor. However, these solutions increase the size of the IO circuit and also result in jitter in the output signals of the IO circuit.